Picloram stability in a sample of forest soil during handling and storage.

Picloram (4-amino-3,5,6-trichloropicolinic acid) is a broad-spectrum herbicide used to control a wide variety of broadleaf and woody vegetation. It is particularly important in forestry (Norris et al. 1983). For both research and monitoring purposes, soil samples are frequently collected and analyzed to determine the persistence and mobility of picloram in the environment. Management, regulatory, and judicial decisions depend on these data; therefore it is essential that results are reliable. Unfortunately, although quality-control and quality-assurance programs are important, sample integrity during handling and storage has received little attention. Most managers of monitoring and research programs expect to complete chemical analyses soon after sample collection. In practice, long delays often occur, yet investigators assume that residue levels found at the time of analysis are the same as those present at the time of sample collection.